Currently known chargers usually can be used only with battery packs with the same capacity. The chargers are configured with a corresponding charging process so as to satisfy the requirements of safety. However, at present, the capacity of battery packs is upgrading rapidly. If an upgraded battery pack is charged by a currently known charger, the battery pack will over heat so that the safety cannot be ensured.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.